A
note from the author: Silicone
impregnated nylon ("silnylon") is one of the most interesting of
the high technology fabrics that's been introduced to the outdoor products
industry over the past several years. So interesting, in fact (at least to
me), that I'm currently working on a separate article entitled
"Silnylon: The Inside Story" that will discuss this material's
history, physical properties, manufacturing processes and legal issues. This
first piece is more narrowly focused and deals primarily with silnylon's use
in backpacking tent floors, an application for which, as it turns out, it's not particularly well suited.

Nevertheless,
because several ultralight shelter manufacturers are using silnylon as a
flooring material, and since buyers frequently complain about the associated
problems (often through Internet discussion forums),
I decided to document this do-it-yourself treatment that can serve as a
single solution to this fabric's three primary floor-related problems. The process described below was developed about
18 months ago and has subsequently undergone extensive field testing to validate its
effectiveness.

Click here if you'd like
to skip the background material and go directly to the treatment description.

Background

As
many backpackers know, silicone impregnated nylon, now commonly used in outdoor product applications, actually began life
in the early 1990's as a
high performance parachute fabric. The original reasons for infusing
silicone into the lightweight nylon base material were primarily to increase
its strength and to render it impermeable to air flow. Fortunately for
today's hikers, this new material also turned out to be waterproof (more or
less), making it an appealing option for use in ultralight tarps, tents,
packs, ponchos, stuff sacks, pack covers and the like. Not long after its adoption in the
parachute industry, companies such as Integral Designs, Tarptent, Six Moon
Designs, Oware, Equinox, and others began offering products
constructed mostly from the "standard" version of silnylon that
typically uses a 30 (or sometimes 40) denier ripstop nylon as a base fabric and that weighs
approximately 1.3 ounces per square yard after silicone impregnation.

In
addition to the standard weight version, silnylon is also available in both lighter and heavier versions that are optimized for specific applications. Likewise, other base
materials, such as microfiber
polyesters and even cotton, can be infused either with silicone or with polymers
such as polyurethane or melamine derivatives, to create finished fabrics whose uses
overlap with those of standard silnylon and that can now be found in products ranging from hot air balloon canopies to racing yacht
sails. Despite the existence of these similar fabrics, however, standard
weight silnylon's unique combination of properties has caused it to emerge as a
favored choice for use in the ultralight floored tents that are the
primary focus of this article.

Looking
forward, 30D silnylon's dominance could be challenged by DuPont's introduction last year of a silicone impregnated Cordura fabric that is said
to be both stronger and lighter than standard weight silnylon. This new
fabric is now being used by companies such as Granite Gear in a line of
ultralight stuff sacks and by Sea to Summit (an Australian company) as a canopy fabric for its
trekking umbrellas. Its suitability for
lightweight shelters, however,
remains to be seen and may ultimately depend upon legal considerations. One
of silnylon's problems (which probably applies to SilCordura as well) is
its flammability, a property that creates compliance issues with the tent fabric
safety laws in some jurisdictions. Fire-retardant versions of silnylon may
become available at some point in the future, but it's my understanding that
no mills produce such a fabric today.

Tent
Floor Problems

When
used as a canopy material for ultralight shelters, 30D silnylon
can work quite well (at least initially). It has a high tear
strength for its weight and is waterproof
enough to repel all but the most robust rains (which can
sometimes penetrate the thin fabric creating a light "misting
effect" inside a shelter). When used for tent floors,
however, this fabric suffers from the disadvantages discussed below when compared with the polyurethane-coated nylons that have
traditionally been employed for this purpose.

The
motivation for this sub-optimal materials selection is simple: weight reduction. The ultralight
segment of the tent market, and perhaps to a lesser extent the mainstream
tent market, currently seems to be driven almost as much by weight factors as it is by
features and functionality. Though the ultimate weights of alternative floor
fabrics in most real-world products may not be that far apart, differences
of only a few ounces can
nonetheless be important to many customers.

Example:The optional sewn-in floor of the popular Tarptent
Squall
ultralight shelter is constructed from standard silnylon and weighs about
5½ ounces, according to the manufacturer. If it were constructed from
even a light version of a traditional polyurethane-coated ripstop
nylon fabric (70D, 6,000mm), the weight of the floor would be about 11½
ounces. Though not immense, the 6 ounce weight difference can still
be non-trivial in this highly competitive market.

Unfortunately,
though lighter in weight than traditional materials, 30D silnylon, when used as
a flooring material, suffers from three
significant problems:

Problem
#1:
The first thing most ultralight shelter buyers notice about silnylon
floors is their extreme "slipperiness". If a tent with such a
floor is pitched on even a slight incline, occupants can quickly find
themselves and their gear sliding into the downhill walls. Besides being
annoying and uncomfortable for users, this concentration of weight is also
hard on the tents since it can create a fair amount of extra stress on
floor seams and stake-out loops, especially on the uphill sides. Ironically,
when considered in connection with the tent's canopy, silnylon's
slipperiness can be an advantage
since it helps, for example, accumulating snow to slide off the roof and
onto the ground, reducing strain on the structure.

Some
ultralight tent manufacturers have suggested solving this problem by
painting stripes of silicone sealer on the inside surface of the silnylon
floor, but if you've tried this procedure, you already know that it doesn't
work very well. Since most of the silnylon remains exposed, the fabric will
usually continue to slip and slide against both objects inside the shelter as
well as against the ground beneath.

Problem
#2:
Standard silnylon is waterproof, but only to a limited degree. Any
"waterproof" fabric will eventually leak if enough pressure is
applied either to the water that's attempting to penetrate from the outside,
or to the dry inside surface of a fabric that's pressing against an external
layer of moisture (the case, for example, with a tent floor). A fabric's
water resistance is usually gauged with a device such
as this that's used to measure a property known as the
"hydrostatic head". This factor reflects the maximum amount of pressure that a fabric can
withstand before it begins to leak and is commonly expressed either as the
height of the water column (usually in millimeters), or as the number of pounds per square
inch of water pressure necessary to force that leakage.

The
polyurethane-coated nylon fabrics used to construct the floors of
conventional tents typically have hydrostatic head values that range from
5,000mm to 10,000mm for reasons that are noted in the next
paragraph. In contrast, the hydrostatic head of standard
weight silnylon, according to most manufacturers' specifications, is only
1 to 2 pounds per square inch, which translates (for consistency
with industry conventions) into a range of 700mm to 1,400mm. In other words,
standard weight silnylon, on average, is less than 15% as water resistant
as conventional tent floors. And that's when new. My own testing suggests
that water resistance can deteriorate significantly with use, findings that
are in line with the parachute industry's acknowledgement that silnylon
typically becomes much more air-permeable with the stresses of usage over time (mandating the eventual retirement
of silnylon parachutes for safety reasons).

So
why does this matter? Well, when
a backpacker sits on a tent floor, most of his/her body weight is
concentrated onto a relatively small area. If a 180 pound man, for example,
is in a "knees-up" sitting position, as much as 90% of his total
body weight (or about 160 pounds) is distributed across perhaps 25 square
inches of "butt print". The man is therefore exerting about 6½
pounds per square inch of weight (or the equivalent of 4,550mm of
hydrostatic head force)
against a fabric whose water resistance is, at most, 1 to 2 pounds per
square inch. Practically speaking then, if a tent floor made from standard
weight silnylon is the only barrier between the man and a soggy patch of
ground beneath, water will probably be forced through the fabric. These
concentrated occupant forces are also the reason that the hydrostatic head
values of conventional tent floor fabrics have traditionally been
5,000mm or higher.

Problem
#3: With a thickness of only about
1½ mils (1 mil = .001 inch),
standard silnylon is pretty thin stuff, a fact that can limit its
durability when used in direct contact with the ground. It is, in fact,
particularly susceptible to micro-punctures and fiber stress fractures when body weight is applied to the top surface. The degree
to which these injuries actually occur depends, to a large extent, on the kind of
surface upon which a tent is pitched. Soft forest duff is fairly easy on
floors as long as sites are preened for sharp obstacles. On the other hand,
hard-packed earth that's covered with a layer of tiny pebbles (like the
soil, for example, that's commonly found at higher elevations in the
Sierras), is particularly hard on tent floors.

Floor
deterioration on these kinds of surfaces is sometimes described in the
backpacking literature as "abrasion", which suggests a kind of
wear that's caused by a shearing movement of the floor against the ground
surface. In fact, however, little or no movement of the floor is usually
required to quickly produce damage with silnylon. The 6½ pounds per square
inch of body force noted above is more than enough to push the sharp edges
of surface gravel well into, or even all the way through, the thin fabric.
Even if not completely punctured, the fabric will likely be weakened enough
to significantly reduce its water resistance.

If
you'd like to test this phenomenon at home, your cement garage floor is a
good place for an experiment, since it's almost inevitably littered with
some of these tiny rocks. If you have a scrap piece of silnylon, place it
onto the hard floor, then sit on it for a bit. You'll find that it doesn't
take much effort to damage the fabric. For these reasons, the use
of a ground cloth under your silnylon tent floor (perhaps
even if you apply the treatment described below) can make sense, especially if you know
that you'll be camping on hard-packed soils.

Treatment
Description

The silicone that's
used for impregnating ripstop nylon fabrics becomes quite inert, chemically
speaking, when it's fully cured. As a result, few substances, other than
adhesives that are themselves silicone-based, will actually bond to
silnylon. The process described below, therefore, uses a silicone sealant as
a foundation that's then diluted with a petroleum solvent (mineral spirits) to form a slurry
that can be painted onto one, or preferably both, side(s) of a silnylon tent
floor or ground cloth. This recipe is similar to those that have been used
for several years to create do-it-yourself silnylon seam sealers, but with a
few important refinements.

The
primary key to success
with this treatment is getting the dilution right. I've tested mixes ranging
from 1:1 (sealant-to-solvent by weight) to 1:15 and believe that a mix of
about 1:3 is probably optimal for tent floors. Adding more sealant simply
adds more weight without significantly improving the quality of the
treatment. Adding more solvent, on the other hand, quickly thins the slurry
to a point where the treatment fails to accomplish the objectives. The only
practical way to make sure that the mix is correct is to weigh the
components, so the use of a scale in the process is critical.

PROBLEMS
SOLVED

When
applied as described, this treatment is colorless, odorless and quite
durable. It
will also:

Completely
eliminate the slipperiness of the original silnylon. The treated
material will have a new "rubbery" feel that will grip both
ground surfaces under the tent, as well as sleeping mats and other gear
inside the shelter even better than traditional
polyurethane floors.

Substantially
enhance the water resistance of the treated surfaces. Though the
home-grown apparatus and procedures
I used for my hydrostatic head tests (and that will be described in
greater length in the upcoming article) are admittedly somewhat crude,
they suggest that if applied evenly to both sides, the treatment can
transform standard 30D silnylon into a floor fabric that's about as
waterproof as those with traditional 6,000mm polyurethane coatings
(i.e., an increase in water resistance of 5 to 7 times).

Approximately
double the effective thickness of standard weight silnylon from 1½
mils to about 3 mils. The new layers of protection on either side
of the fabric, along with the ability of their rubbery surfaces to absorb
minor environmental insults without sustaining serious damage, can significantly
improve the resistance of treated surfaces to punctures and other stress
wounds.

WEIGHT

Aside
from the small cost of materials and the time required for application,
about the only downside to the treatment is that it adds a little weight to
the tent. If
applied to both the upper and lower surfaces (recommended), the floor will
probably become 2 or 3 ounces heavier as the silnylon fabric gains about ¾ ounce per square yard. Accordingly, the new fabric weight will be
approximately 2 ounces per square yard, rather than the original
1.3 ounces. Even at this weight, however, the treated floor will still
be lighter than most 70D polyurethane-coated fabrics by 25% or more. In
addition, some users will probably decide that their silnylon floors are now
sufficiently "trail hardened" that it's no longer necessary to
carry separate ground cloths to protect them, thereby saving the weight of
the coating and then some.

OTHER
ADVANTAGES

In
addition to solving the three primary problems noted above, the finished floors will enjoy a couple of other
advantages over their conventional polyurethane-coated brethren:

When
exposed to moisture, a silnylon floor (whether treated or not) will
typically absorb much less water than a traditional floor. That's the
case because polyurethane coatings are usually applied only to inside
surfaces, which means that the uncoated, hydrophilic (water loving)
nylon fibers on the outside are free to soak up as much water as they
can carry. That tends to be true (in my experience) even if a durable
water repellant (DWR) is initially applied to the outside
surface, since these repellants often wear off tent floors quickly with use. From a
practical point of view, although the absorbed moisture may not actually
penetrate the polyurethane floor while the tent is pitched in camp, it will add weight on the
trail.

Over
time, polyurethane coatings can sometimes peel away from the nylon base
fabrics or otherwise become damaged with use. Since the polyurethane
coating process is not generally considered to be user-friendly, tents
with these afflictions must often be returned to the factory for
repairs. The treatment described here, however, can be easily re-applied
(in whole or in part) whenever necessary.

All
factors considered, and after a year and a half of testing, the bottom line
for me is that I now much prefer a silnylon tent floor that's been
treated with the process described here over a conventional,
polyurethane-coated floor.

The
key ingredients required for this process are simple and inexpensive. They
include:

A
tube of clear, general-purpose silicone sealant. You'll need at least
2½ to 3 fluid ounces, or possibly more, depending on your floor size.
Almost any brand will do, but you'll probably find that the ubiquitous
GE products, at about $1.00 per fluid ounce, are more expense than most
others. In contrast, the 10.1oz Mainstays brand that's currently sold in caulking
tube form at
Wal-Mart for $2.17 (pictured above) works well and costs only about
20% as much. Its packaging is also transparent on one side, so that it's easy to see how much sealant has been used (why don't all
manufacturers do this?). If you select this option,
you'll also need a caulking gun ($1.54 at Wal-Mart) and a nail or
similar object to plug the partially-used caulking tube after
use.
Important: For this ingredient, make sure that you use
a true silicone sealant. There are other clear adhesives that
have a similar appearance, but that are not actually silicone-based.
These other products will not work for this treatment, so make sure that
you read labels carefully.

A
quart of low-odor mineral spirits (sometimes called "Stoddard
solvent"). Mineral spirits is a general purpose, petroleum-based
solvent that's normally used as a paint thinner. The Kleen-Strip brand
is currently sold in Wal-Mart's paint department for $3.17 and may come
either in a metal can (pictured above) or a clear plastic bottle.

Mineral spirits is also available in a traditional formula (I guess I'd call it
"high-odor") that you want to avoid. Besides being unpleasant to work
with, this type will also impart a strong petroleum smell to the finished
treatment that will take a long time (many weeks) to dissipate.
Important: So to
repeat, make sure you use low-odor (sometimes called
"odorless") mineral spirits. This version costs a dollar
or two more per quart than the older formula, but is well worth the
extra expense for this treatment.

A
metal can (16 oz to 32 oz) for mixing the ingredients. Some
plastic containers may be OK too, but it's also possible that the
mineral spirits could react with certain polymers, so a metal container
is probably the safest choice. You may also need a second container for
cleaning your brush and/or for disposing of excess slurry.

Something
with which to stir the ingredients. A hardware store wooden paint paddle (often
free) split vertically into 2 strips with a box-cutter works great.

A
paint brush, 1½" to 2" wide, to spread the slurry mix
onto your tent floor surfaces. You'll want to make sure that the brush is
OK to use with oil-based paints so that the mineral spirits won't
dissolve the bristles. A foam brush that's oil-base safe might also
work, though I haven't tried it myself. Don't spend a lot on this brush,
however, since you'll probably end up discarding it.

A
scale that's reasonably accurate in the 0-to-5 pound range. I use a
postage scale (pictured above) that handles up to 2 pounds. Most kitchen food
scales also work well. If you're an ultralight backpacker, then I
suspect that you probably already have a suitable option at
hand.

A
supply of paper towels.

And
finally,
you'll need a tarp or reasonably thick painting drop cloth that's large
enough to place under your tent for protection while you apply the
treatment. During the process, you'll probably need to get on your hands
and knees on top of the fabric in order to reach the areas you wish to
coat. If you place your tent directly on say, a garage floor, you could
end up micro-puncturing the canopy with the tiny particles of gravel
that are described
above.

Treatment
Process

Note:
If you're uncertain about this process, you may wish to test it first on
a scrap piece of silnylon or on a small section of your tent floor before
committing to covering an entire surface. Small quantities of silnylon
that can be used for testing purposes are available from a number of online
sources, including those
mentioned here.

Step
1: Prepare your tent floor to be painted. To coat the interior
side, it may be easiest to set up the tent as you normally would on
reasonably firm ground, with a tarp or ground cloth underneath to protect
the floor from punctures. Alternatively, you can turn the tent inside out
through the doorway to expose the interior floor that can then be laid out
flat on your work surface for coating (again, making sure there's a tarp
beneath to protect it). This same approach can also be used to coat the
exterior surface if it's not possible to pitch the tent inside out. And of
course, make sure that the surface about to be painted is clean and dry, and
that the work area is well ventilated.

Step
2: Mix your first batch of slurry. To do so, first place your
empty mixing container on the scale, then adjust the weight (probably using
a knob located somewhere on the scale) back to zero. Now squeeze
1 ounce of silicone sealant into the bottom of the can. Re-adjust the
total scale weight back to zero again, then add 3 ounces (by weight) of
mineral spirits. Finally,
stir the sealant until it's completely dissolved in the mineral spirits.
This process can take quite a while - perhaps 3 or 4 minutes or
more, since
the sealant tends to dissolve slowly. Keep stirring though, until the mix is
uniformly runny.

TIPS:
It's best not to mix too much slurry at one time, since it can
begin to cure (dry) in the can before you have time to paint it onto the
fabric. If you're treating a relatively large surface, you can mix
additional batches as necessary. Also, if your scale can't be re-adjusted to zero as described above
(a convenience, but not a necessity), you can simply add the weights of
each component to the cumulative weight up to that point in order to
maintain the
right mix.

Step
3: Using your brush, paint the surface of the fabric in sections,
as evenly as possible, using overlapping strokes. Most floors will probably require only
10 or 15 minutes to cover completely. When you're finished with the
first side, clean any excess slurry out of your mixing container and dispose
of it. You can then rinse your brush with mineral spirits to clean. The new
treated surface will probably be dry enough to touch or to move in 30 to 45
minutes. To be safe, however, it's probably best to allow the first surface
to cure overnight before turning your tent inside out and coating the
opposite surface.

TIPS:
If you use a caulking gun for the sealant, use a nail or similar object to
stopper the partially-used tube after painting sessions. It's also best to
remove the tube from the gun, since it's sometimes possible for sealant to
squeeze backwards into the chamber around the gun's plunger. When it cures,
this "blow-back" sealant can effectively freeze the tube into the
gun, making the two components very difficult to separate from one another.

Step
4: When you and your tent are both ready, repeat steps 1 to
3 for the second surface. One coat on each side will probably be sufficient
as long as a 1:3 mix ratio is maintained.

Other
Notes

The
treatment described here could, of course, be used to enhance the water
resistance of other silnylon products. Stuff sacks are one possibility
that come to mind, though you'd probably want to limit the treatment to
the outside surface only, since the high "friction factor" of
the coating might make it difficult to get things in and out of the sack
if the interior were treated.

If
your tent floor is subjected to a lot of use on gravel or other abrasive
surfaces, you may find it necessary to re-coat the floor at some point.
To minimize the cumulative weight impact of the treatments, you could
probably get by painting just the high-wear portions of the floor,
and/or by using
a slightly more diluted solution (perhaps 1:5). I haven't tried
re-treatment myself, however, so you're kind of on your own here.

If
you happen to build your own shelters and are wondering if you should
treat the floor before or after it's sewn into the tent, you might want
to know that, at least with my machine (a Brother model XR-46 without a
walking foot), the
post-treated fabric feeds through the machine with no problems, making
possible the more convenient option of treating-before-sewing.

To
the best of my knowledge, this process (at least using these ingredients)
only works well on silnylon. If applied to other fabrics, the treatment
will usually rub off with little effort.

Even
with this treatment, you still may elect to use a ground cloth under
your tent floor, if only to help keep it clean. While there are plenty of
options out there, I've had particularly good luck with kite Tyvek (Type
#1443R). At 1.25 oz per square yard, it weighs even less than standard
silnylon, is quite tough, not slippery, and fairly water resistant (though not completely
waterproof). More information about its properties and
availability can be found
here.

And as you probably already know, any ground cloth should be slightly smaller than your tent's footprint so that exposed edges
don't channel rain under the floor. This advice only works, however, if the
ground cloth remains more or less centered under the tent. To help keep
it in that position (especially under high wind conditions) I'd recommend
attaching lightweight cord loops of an appropriate length to each of the ground cloth's
corners (Kelty Triptease or nylon parachute cord both work well for this
purpose).
These loops can then be hooked onto to the tent's existing stakes to
anchor the ground cloth in place. With kite Tyvek or other lightweight
fabrics, the strongest way to attach these cord loops is probably to tie
them (rather than sew them) into the fabric using a knot of your choice.

In
the spirit of collaboration with your fellow backpackers, if
you try this treatment, please let us know about your experiences through the
feedback forum. Your comments and suggestions will undoubtedly help to
improve the process for everyone... Thanks, Jim Wood.